This invention relates to a robot control apparatus having a palletizing function.
Generally, in order for a robot A shown in FIG. 3 to carry out a palletizing operation to automatically stack and unstack workpieces, a robot control apparatus having a prescribed palletizing function is required. This robot is constructed for control along six axes, namely a .theta. axis, V axis, U axis, .alpha. axis, .beta. axis and .gamma. axis, and performs palletizing by gripping workpieces by means of a hand.
An example of a palletizing operation will now be described with reference to FIGS. 4 through 6. If workpieces W are to be stacked in the n rows, m columns and l levels shown in FIG. 4 by a palletizing operation, first the palletizing positions P1, Q111, Qn11, Q1m1, Qnm1, Q11l, R1 are defined wherein
n: Number of Workpiece Rows PA1 m: Number of Workpiece Columns PA1 l: Number of Workpiece Levels PA1 P1: Point Above First Row, First Column PA1 Q11l: Workpiece Position in First Row, First Column, l'th Level PA1 Q1m1: Workpiece Position in First Row, m-th Column, First Level PA1 Qnm1: Workpiece Position in n-th Row, m-th Column, First Level PA1 Q11l: Workpiece Positional in First Row, First Column, First Level PA1 R1: Palletizing End Point.
Then pelletizing is executed by software prepared in accordance with a predetermined program.
By way of example, an operation for stacking a workpiece at a point Qijk shown in FIG. 6 is performed through the following sequence:
(1) The robot hand is moved from a position at point 0, which is occupied prior to the start of palletizing, to a point Pij. The point Pij is set in such a manner that vectors Q111P1 and Qij1Pij will be equal.
(2) The hand is moved along a straight line from the point Pij to the point Qijk.
(3) The workpiece is stacked at the point Qijk.
(4) The hand is moved along a straight line from the point Qijk to a point Rij. The position of Rij is set in such a manner that vectors Q111R1 and Qij1Rij will be equal.
(5) The hand is moved from the point Rij to a position S which the hand occupies at the conclusion of palletizing.
The attitude of the hand at the points Pij, Rij is made to coincide with that at points P1, R1, and the attitude of the hand at the point Qijk is made to coincide with that at point Q111.
Thus, with a robot control apparatus having this conventional palletizing function, the robot is controlled on the assumption that workpieces of the same shape as shown in FIG. 4 are to be stacked and unstacked in a fixed pattern.
However, there are instances when it is necessary to perform palletizing while changing the attitude of the robot hand from one level to the next even though the workpieces are identical in shape, as in a case where a palletizing reference position shifts in accordance with stacking, as with automobile doors Wo shown in FIG. 7(a), or in a case where workpieces W1, W2 having different sizes as shown in FIG. 7(b) are stacked, or workpieces W3, W4, the sizes of which differ from one level to the next, are stacked, as depicted in FIG. 7(c). Furthermore, in order to control movement in such a manner that the robot hand will not interfere with a workpiece stacked previously, it is necessary to prepare a variety of motion patterns in advance and perform the operation while changing the motion pattern for each workpiece. However, a robot control apparatus having the conventional palletizing function cannot cope with these situations.